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Elevator control system
Manually-controlled elevator Early elevators had no automatic landing positioning. Elevators were operated by elevator operators using a motor controller. The controller was contained within a cylindrical container about the size and shape of a cake container and this was operated via a projecting handle. This allowed some control over the energy supplied to the motor (located at the top of the elevator shaft or beside the bottom of the elevator shaft) and so enabled the elevator to be accurately positioned — if the operator was sufficiently skilled. More typically the operator would have to "jog" the control to get the elevator reasonably close to the landing point and then direct the outgoing and incoming passengers to "watch the step". Some older freight elevators are controlled by switches operated by pulling on adjacent ropes. Safety interlocks ensure that the inner and outer doors are closed before the elevator is allowed to move. Later on, Otis introduced manually controlled elevators with automatic leveling. The operator could still controll the speed, but when they released the controller the elevator levelled smoothly to the nearest floor in that direction. This was one of the first steps towards full automatic control of elevators. Passenger-056_medium.jpeg|The cylindrical controller from an antique Otis elevator Automatic-controlled elevator Relay-controlled Automatic elevators began to appear as early as the 1920s. These electromechanical systems used relay logic circuits of increasing complexity to control the speed, position and door operation of an elevator or bank of elevators. Elevators with relay logics have a device called "floor selector". Mechanical floor selectors use analog controls and many moving parts to determine the car’s position. The floor selector uses magnetic tapes (often called selector tape) which is attached at the top of the car. When the elevator is moving, so does the tape, which moves the mechanical gears on the floor selector. Otis introduces the world's first fully automatic relay logic controlled elevator system in 1924 called "Signal Control". Later in 1937, Otis introduce the Peak Period Control to automatically schedule elevator service during high-demand periods. It helped reduce the waiting time on any given floor by coordinating the movement of the building’s elevators. Automatic elevators in the 1940s has the ability to change the car speeds, adjust their schedules to suit traffic demand and bypassing floors when the car is fully loaded. An example of this was the Otis "Autotronic Elevator" system which was introduced in 1948. A similar elevator system is also invented by Westinghouse in the 1950s called "Selectomatic". Relay-controlled elevator systems remained common until right up until the 1980s, and their gradual replacement with solid-state microprocessor-based controls which are now the industry standard. Express Lift relay logics 60s.jpg|Express Lift relay logic cabinet. The object on the bottom is a mechanical floor selector. Express Lift relay logics 60s (2).jpg|A closer look of the older Express Lift relays. Otis relay logics.jpg|Cabinet full of old Otis relays. Schindler 70s relay logic.jpg|Schindler elevator relay cabinet from the 1970s. Schindler elevator floor selector.jpg|Schindler floor selector from the 1970s. Microprocessor control Elevators with microprocessor control first appeared in 1979 when Otis, introduce the Elevonic 101 elevator. This elevator system uses microprocessor to control every aspect of the elevator operation. Beyond the passenger interaction are a series of sensors, controllers, sequences of operation and real-time calculations or algorithms that balance passenger demand and car availability. Elevator sensors provide data on car positions, car moving direction, loads, door status, hall calls, car calls, pending up hall and down hall calls, number of runs per car, alarms, etc. The elevator controllers are typically Programmable Logic Controllers (PLC) that may be configured for a single car, multiple cars or sized by the number of stops and including interfaces for monitoring, voice synthesizers, etc. The controller may also have a function enabling the testing the systems without shutdown of the elevator. Modern elevator controller cabinet.jpg|A modern elevator microprocessor controller cabinet. Schindler 80s elevator logic controller.jpg|Schindler microprocessor controller from the early 1980s. Elevator PLC device.jpg|PLC device (manufactured by Mitsubishi). Elevator board.jpg|Inside modern elevator microprocessor controller cabinet. Elevator destination dispatch system Main article: Elevator Destination Dispatch Elevator remote monitoring system Most of the relevant data from the controllers is related to car activity: the car position, direction, car load and door status. From that data a management system consisting of a workstation and manufacturer’s software application can then create metrics for a group or particular car such as total number of door openings, number of runs per car or call, up and down hall calls, etc. Some of the key performance indicators that facility managers would look for may include passenger “wait times during peak time’ or “time for a car to go from bottom to the top floor”. These metrics may indicate inadequate controls, misconfiguration or even equipment malfunction. Many elevator manufacturers can now provide remote monitoring of the equipment through Software as a Service (SaaS). The monitoring looks for malfunctions or abnormal operating parameters and either dispatches a technician or alerts the building owner. Some manufacturers provide customer dashboards accessible via a web browser and provide owners with information such as performance summaries and maintenance histories. This may work well for building owners who may not have that specialized expertise on staff. Some notable elevator remote monitoring systems are the Otis REM, Schindler Servitel, Kone's KoneXion, Mitsubishi's MelEye, etc. Category:Elevator Category:Elevator controls Category:Elevator systems